We installed a marble shower wall, and the contractor used an acid to clean it. We had it professionally repolished, but it keeps getting etched after we take a shower. What’s causing the etching and how do we correct it?

I will assume you are not cleaning it with acid cleaners. There is a possibility that there is some residual acid in the grout or the pores of the stone that bleeds out when you take a shower. Try rinsing the shower wall with a solution of baking soda and water. Prepare approximately one cup of baking soda to one gallon of water, and flood the wall several times with this solution. If there is any residual acid, this solution should neutralize it.